CVE-2024-26976 (GCVE-0-2024-26976)

Vulnerability from cvelistv5 – Published: 2024-05-01 05:20 – Updated: 2025-05-04 09:01
VLAI?
Title
KVM: Always flush async #PF workqueue when vCPU is being destroyed
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: Always flush async #PF workqueue when vCPU is being destroyed Always flush the per-vCPU async #PF workqueue when a vCPU is clearing its completion queue, e.g. when a VM and all its vCPUs is being destroyed. KVM must ensure that none of its workqueue callbacks is running when the last reference to the KVM _module_ is put. Gifting a reference to the associated VM prevents the workqueue callback from dereferencing freed vCPU/VM memory, but does not prevent the KVM module from being unloaded before the callback completes. Drop the misguided VM refcount gifting, as calling kvm_put_kvm() from async_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will result in deadlock. async_pf_execute() can't return until kvm_put_kvm() finishes, and kvm_put_kvm() can't return until async_pf_execute() finishes: WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm] Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Workqueue: events async_pf_execute [kvm] RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm] Call Trace: <TASK> async_pf_execute+0x198/0x260 [kvm] process_one_work+0x145/0x2d0 worker_thread+0x27e/0x3a0 kthread+0xba/0xe0 ret_from_fork+0x2d/0x50 ret_from_fork_asm+0x11/0x20 </TASK> ---[ end trace 0000000000000000 ]--- INFO: task kworker/8:1:251 blocked for more than 120 seconds. Tainted: G W 6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:kworker/8:1 state:D stack:0 pid:251 ppid:2 flags:0x00004000 Workqueue: events async_pf_execute [kvm] Call Trace: <TASK> __schedule+0x33f/0xa40 schedule+0x53/0xc0 schedule_timeout+0x12a/0x140 __wait_for_common+0x8d/0x1d0 __flush_work.isra.0+0x19f/0x2c0 kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm] kvm_arch_destroy_vm+0x78/0x1b0 [kvm] kvm_put_kvm+0x1c1/0x320 [kvm] async_pf_execute+0x198/0x260 [kvm] process_one_work+0x145/0x2d0 worker_thread+0x27e/0x3a0 kthread+0xba/0xe0 ret_from_fork+0x2d/0x50 ret_from_fork_asm+0x11/0x20 </TASK> If kvm_clear_async_pf_completion_queue() actually flushes the workqueue, then there's no need to gift async_pf_execute() a reference because all invocations of async_pf_execute() will be forced to complete before the vCPU and its VM are destroyed/freed. And that in turn fixes the module unloading bug as __fput() won't do module_put() on the last vCPU reference until the vCPU has been freed, e.g. if closing the vCPU file also puts the last reference to the KVM module. Note that kvm_check_async_pf_completion() may also take the work item off the completion queue and so also needs to flush the work queue, as the work will not be seen by kvm_clear_async_pf_completion_queue(). Waiting on the workqueue could theoretically delay a vCPU due to waiting for the work to complete, but that's a very, very small chance, and likely a very small delay. kvm_arch_async_page_present_queued() unconditionally makes a new request, i.e. will effectively delay entering the guest, so the remaining work is really just: trace_kvm_async_pf_completed(addr, cr2_or_gpa); __kvm_vcpu_wake_up(vcpu); mmput(mm); and mmput() can't drop the last reference to the page tables if the vCPU is still alive, i.e. the vCPU won't get stuck tearing down page tables. Add a helper to do the flushing, specifically to deal with "wakeup all" work items, as they aren't actually work items, i.e. are never placed in a workqueue. Trying to flush a bogus workqueue entry rightly makes __flush_work() complain (kudos to whoever added that sanity check). Note, commit 5f6de5cbebee ("KVM: Prevent module exit until al ---truncated---
Severity ?
7 (High)
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE
  • CWE-400 - Uncontrolled Resource Consumption
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < ab2c2f5d9576112ad22cfd3798071cb74693b1f5 (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 82e25cc1c2e93c3023da98be282322fc08b61ffb (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < f8730d6335e5f43d09151fca1f0f41922209a264 (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 83d3c5e309611ef593e2fcb78444fc8ceedf9bac (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < b54478d20375874aeee257744dedfd3e413432ff (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < a75afe480d4349c524d9c659b1a5a544dbc39a98 (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 4f3a3bce428fb439c66a578adc447afce7b4a750 (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < caa9af2e27c275e089d702cfbaaece3b42bca31b (git)
Affected: af585b921e5d1e919947c4b1164b59507fe7cd7b , < 3d75b8aa5c29058a512db29da7cbee8052724157 (git)
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    Linux Linux Affected: 2.6.38
Unaffected: 0 , < 2.6.38 (semver)
Unaffected: 4.19.312 , ≤ 4.19.* (semver)
Unaffected: 5.4.274 , ≤ 5.4.* (semver)
Unaffected: 5.10.215 , ≤ 5.10.* (semver)
Unaffected: 5.15.154 , ≤ 5.15.* (semver)
Unaffected: 6.1.84 , ≤ 6.1.* (semver)
Unaffected: 6.6.24 , ≤ 6.6.* (semver)
Unaffected: 6.7.12 , ≤ 6.7.* (semver)
Unaffected: 6.8.3 , ≤ 6.8.* (semver)
Unaffected: 6.9 , ≤ * (original_commit_for_fix)
Create a notification for this product.
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Always flush async #PF workqueue when vCPU is being destroyed\n\nAlways flush the per-vCPU async #PF workqueue when a vCPU is clearing its\ncompletion queue, e.g. when a VM and all its vCPUs is being destroyed.\nKVM must ensure that none of its workqueue callbacks is running when the\nlast reference to the KVM _module_ is put.  Gifting a reference to the\nassociated VM prevents the workqueue callback from dereferencing freed\nvCPU/VM memory, but does not prevent the KVM module from being unloaded\nbefore the callback completes.\n\nDrop the misguided VM refcount gifting, as calling kvm_put_kvm() from\nasync_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will\nresult in deadlock.  async_pf_execute() can\u0027t return until kvm_put_kvm()\nfinishes, and kvm_put_kvm() can\u0027t return until async_pf_execute() finishes:\n\n WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm]\n Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass\n CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G        W          6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n Workqueue: events async_pf_execute [kvm]\n RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm]\n Call Trace:\n  \u003cTASK\u003e\n  async_pf_execute+0x198/0x260 [kvm]\n  process_one_work+0x145/0x2d0\n  worker_thread+0x27e/0x3a0\n  kthread+0xba/0xe0\n  ret_from_fork+0x2d/0x50\n  ret_from_fork_asm+0x11/0x20\n  \u003c/TASK\u003e\n ---[ end trace 0000000000000000 ]---\n INFO: task kworker/8:1:251 blocked for more than 120 seconds.\n       Tainted: G        W          6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\n \"echo 0 \u003e /proc/sys/kernel/hung_task_timeout_secs\" disables this message.\n task:kworker/8:1     state:D stack:0     pid:251   ppid:2      flags:0x00004000\n Workqueue: events async_pf_execute [kvm]\n Call Trace:\n  \u003cTASK\u003e\n  __schedule+0x33f/0xa40\n  schedule+0x53/0xc0\n  schedule_timeout+0x12a/0x140\n  __wait_for_common+0x8d/0x1d0\n  __flush_work.isra.0+0x19f/0x2c0\n  kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm]\n  kvm_arch_destroy_vm+0x78/0x1b0 [kvm]\n  kvm_put_kvm+0x1c1/0x320 [kvm]\n  async_pf_execute+0x198/0x260 [kvm]\n  process_one_work+0x145/0x2d0\n  worker_thread+0x27e/0x3a0\n  kthread+0xba/0xe0\n  ret_from_fork+0x2d/0x50\n  ret_from_fork_asm+0x11/0x20\n  \u003c/TASK\u003e\n\nIf kvm_clear_async_pf_completion_queue() actually flushes the workqueue,\nthen there\u0027s no need to gift async_pf_execute() a reference because all\ninvocations of async_pf_execute() will be forced to complete before the\nvCPU and its VM are destroyed/freed.  And that in turn fixes the module\nunloading bug as __fput() won\u0027t do module_put() on the last vCPU reference\nuntil the vCPU has been freed, e.g. if closing the vCPU file also puts the\nlast reference to the KVM module.\n\nNote that kvm_check_async_pf_completion() may also take the work item off\nthe completion queue and so also needs to flush the work queue, as the\nwork will not be seen by kvm_clear_async_pf_completion_queue().  Waiting\non the workqueue could theoretically delay a vCPU due to waiting for the\nwork to complete, but that\u0027s a very, very small chance, and likely a very\nsmall delay.  kvm_arch_async_page_present_queued() unconditionally makes a\nnew request, i.e. will effectively delay entering the guest, so the\nremaining work is really just:\n\n        trace_kvm_async_pf_completed(addr, cr2_or_gpa);\n\n        __kvm_vcpu_wake_up(vcpu);\n\n        mmput(mm);\n\nand mmput() can\u0027t drop the last reference to the page tables if the vCPU is\nstill alive, i.e. the vCPU won\u0027t get stuck tearing down page tables.\n\nAdd a helper to do the flushing, specifically to deal with \"wakeup all\"\nwork items, as they aren\u0027t actually work items, i.e. are never placed in a\nworkqueue.  Trying to flush a bogus workqueue entry rightly makes\n__flush_work() complain (kudos to whoever added that sanity check).\n\nNote, commit 5f6de5cbebee (\"KVM: Prevent module exit until al\n---truncated---"
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          "url": "https://git.kernel.org/stable/c/3d75b8aa5c29058a512db29da7cbee8052724157"
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    "dateReserved": "2024-02-19T14:20:24.203Z",
    "dateUpdated": "2025-05-04T09:01:18.606Z",
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\"https://git.kernel.org/stable/c/83d3c5e309611ef593e2fcb78444fc8ceedf9bac\"}, {\"url\": \"https://git.kernel.org/stable/c/b54478d20375874aeee257744dedfd3e413432ff\"}, {\"url\": \"https://git.kernel.org/stable/c/a75afe480d4349c524d9c659b1a5a544dbc39a98\"}, {\"url\": \"https://git.kernel.org/stable/c/4f3a3bce428fb439c66a578adc447afce7b4a750\"}, {\"url\": \"https://git.kernel.org/stable/c/caa9af2e27c275e089d702cfbaaece3b42bca31b\"}, {\"url\": \"https://git.kernel.org/stable/c/3d75b8aa5c29058a512db29da7cbee8052724157\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nKVM: Always flush async #PF workqueue when vCPU is being destroyed\\n\\nAlways flush the per-vCPU async #PF workqueue when a vCPU is clearing its\\ncompletion queue, e.g. when a VM and all its vCPUs is being destroyed.\\nKVM must ensure that none of its workqueue callbacks is running when the\\nlast reference to the KVM _module_ is put.  Gifting a reference to the\\nassociated VM prevents the workqueue callback from dereferencing freed\\nvCPU/VM memory, but does not prevent the KVM module from being unloaded\\nbefore the callback completes.\\n\\nDrop the misguided VM refcount gifting, as calling kvm_put_kvm() from\\nasync_pf_execute() if kvm_put_kvm() flushes the async #PF workqueue will\\nresult in deadlock.  async_pf_execute() can\u0027t return until kvm_put_kvm()\\nfinishes, and kvm_put_kvm() can\u0027t return until async_pf_execute() finishes:\\n\\n WARNING: CPU: 8 PID: 251 at virt/kvm/kvm_main.c:1435 kvm_put_kvm+0x2d/0x320 [kvm]\\n Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel kvm irqbypass\\n CPU: 8 PID: 251 Comm: kworker/8:1 Tainted: G        W          6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\\n Workqueue: events async_pf_execute [kvm]\\n RIP: 0010:kvm_put_kvm+0x2d/0x320 [kvm]\\n Call Trace:\\n  \u003cTASK\u003e\\n  async_pf_execute+0x198/0x260 [kvm]\\n  process_one_work+0x145/0x2d0\\n  worker_thread+0x27e/0x3a0\\n  kthread+0xba/0xe0\\n  ret_from_fork+0x2d/0x50\\n  ret_from_fork_asm+0x11/0x20\\n  \u003c/TASK\u003e\\n ---[ end trace 0000000000000000 ]---\\n INFO: task kworker/8:1:251 blocked for more than 120 seconds.\\n       Tainted: G        W          6.6.0-rc1-e7af8d17224a-x86/gmem-vm #119\\n \\\"echo 0 \u003e /proc/sys/kernel/hung_task_timeout_secs\\\" disables this message.\\n task:kworker/8:1     state:D stack:0     pid:251   ppid:2      flags:0x00004000\\n Workqueue: events async_pf_execute [kvm]\\n Call Trace:\\n  \u003cTASK\u003e\\n  __schedule+0x33f/0xa40\\n  schedule+0x53/0xc0\\n  schedule_timeout+0x12a/0x140\\n  __wait_for_common+0x8d/0x1d0\\n  __flush_work.isra.0+0x19f/0x2c0\\n  kvm_clear_async_pf_completion_queue+0x129/0x190 [kvm]\\n  kvm_arch_destroy_vm+0x78/0x1b0 [kvm]\\n  kvm_put_kvm+0x1c1/0x320 [kvm]\\n  async_pf_execute+0x198/0x260 [kvm]\\n  process_one_work+0x145/0x2d0\\n  worker_thread+0x27e/0x3a0\\n  kthread+0xba/0xe0\\n  ret_from_fork+0x2d/0x50\\n  ret_from_fork_asm+0x11/0x20\\n  \u003c/TASK\u003e\\n\\nIf kvm_clear_async_pf_completion_queue() actually flushes the workqueue,\\nthen there\u0027s no need to gift async_pf_execute() a reference because all\\ninvocations of async_pf_execute() will be forced to complete before the\\nvCPU and its VM are destroyed/freed.  And that in turn fixes the module\\nunloading bug as __fput() won\u0027t do module_put() on the last vCPU reference\\nuntil the vCPU has been freed, e.g. if closing the vCPU file also puts the\\nlast reference to the KVM module.\\n\\nNote that kvm_check_async_pf_completion() may also take the work item off\\nthe completion queue and so also needs to flush the work queue, as the\\nwork will not be seen by kvm_clear_async_pf_completion_queue().  Waiting\\non the workqueue could theoretically delay a vCPU due to waiting for the\\nwork to complete, but that\u0027s a very, very small chance, and likely a very\\nsmall delay.  kvm_arch_async_page_present_queued() unconditionally makes a\\nnew request, i.e. will effectively delay entering the guest, so the\\nremaining work is really just:\\n\\n        trace_kvm_async_pf_completed(addr, cr2_or_gpa);\\n\\n        __kvm_vcpu_wake_up(vcpu);\\n\\n        mmput(mm);\\n\\nand mmput() can\u0027t drop the last reference to the page tables if the vCPU is\\nstill alive, i.e. the vCPU won\u0027t get stuck tearing down page tables.\\n\\nAdd a helper to do the flushing, specifically to deal with \\\"wakeup all\\\"\\nwork items, as they aren\u0027t actually work items, i.e. are never placed in a\\nworkqueue.  Trying to flush a bogus workqueue entry rightly makes\\n__flush_work() complain (kudos to whoever added that sanity check).\\n\\nNote, commit 5f6de5cbebee (\\\"KVM: Prevent module exit until al\\n---truncated---\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"4.19.312\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.4.274\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.215\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.154\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.84\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.24\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.7.12\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.8.3\", \"versionStartIncluding\": \"2.6.38\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.9\", \"versionStartIncluding\": \"2.6.38\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2025-05-04T09:01:18.606Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2024-26976\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2025-05-04T09:01:18.606Z\", \"dateReserved\": \"2024-02-19T14:20:24.203Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-05-01T05:20:24.025Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.1"
    }
  }
}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Detection rules are retrieved from Rulezet.